Bottom Line:
Between-reservoir comparisons indicated an advanced eutrophication at Baldeneysee and Hengsteysee and the small-scale within-reservoir variations of component communities provided evidence that larval trematodes may have reflected spatial bird aggregations (infection 'hot spots').Two life history groupings of dominant species, the 'cyprinid' and 'anatid' parasites, that depict two aspects of progressive eutrophication in this mature reservoir system, were identified.Whereas variations in trematode community diversity and abundance may indicate the degree of eutrophication on a larger scale (among reservoirs), the infection rates of the two life history groups of dominant species, the 'cyprinid' and 'anatid' assemblages, may be particularly useful in depicting environmental variability, eutrophication effects and infection 'hot spots' on smaller spatial scales.

Background: Analysis of the data available from traditional faunistic approaches to mollusc-trematode systems covering large spatial and/or temporal scales in Europe convinced us that a parasite community approach in well-defined aquatic ecosystems is essential for the substantial advancement of our understanding of the parasite response to anthropogenic pressures in urbanised areas which are typical on a European scale. Here we describe communities of larval trematodes in two lymnaeid species, Radix auricularia and Lymnaea stagnalis in four man-made interconnected reservoirs of the Ruhr River (Germany) focusing on among- and within-reservoir variations in parasite prevalence and component community composition and structure.

Results: The mature reservoir system on the Ruhr River provides an excellent environment for the development of species-rich and abundant trematode communities in Radix auricularia (12 species) and Lymnaea stagnalis (6 species). The lake-adapted R. auricularia dominated numerically over L. stagnalis and played a major role in the trematode transmission in the reservoir system. Both host-parasite systems were dominated by bird parasites (13 out of 15 species) characteristic for eutrophic water bodies. In addition to snail size, two environmental variables, the oxygen content and pH of the water, were identified as important determinants of the probability of infection. Between-reservoir comparisons indicated an advanced eutrophication at Baldeneysee and Hengsteysee and the small-scale within-reservoir variations of component communities provided evidence that larval trematodes may have reflected spatial bird aggregations (infection 'hot spots'). Two life history groupings of dominant species, the 'cyprinid' and 'anatid' parasites, that depict two aspects of progressive eutrophication in this mature reservoir system, were identified.

Conclusions: We conclude that trematode communities in the lake-adapted R. auricularia are better suited for monitoring the effect of environmental change on host-parasite associations in the reservoir system on the Ruhr River and other similar systems due to the important role of this host in trematode transmission in lakes. Whereas variations in trematode community diversity and abundance may indicate the degree of eutrophication on a larger scale (among reservoirs), the infection rates of the two life history groups of dominant species, the 'cyprinid' and 'anatid' assemblages, may be particularly useful in depicting environmental variability, eutrophication effects and infection 'hot spots' on smaller spatial scales.

Figure 1: Map of the area and the reservoir system studied on Ruhr River.

Mentions:
Molluscs were sampled at four out of the five artificial reservoirs on the river Ruhr: Hengsteysee, Harkortsee, Kemnader See and Baldeneysee (see map in Fig. 1 and Table 1 for details). Baldeneysee is the largest of the four, noticeably longer and with more than double the volume of the other reservoirs which are of similar size (Table 1). All reservoirs were constructed (three as early as the 1930's) as deposit reservoirs of sediments from the inflowing rivers Lenne and Volme and natural water purification. With the construction and development of more effective sewage treatment plants along the Ruhr the initial function of water purification has become secondary; currently the reservoirs of the Ruhr River serve for drinking water and hydropower supply and recreation. The shallow nature of these water bodies has gradually resulted in volume loss due to the deposition and accumulation of sediments. As a restoration measure, sediment removal has been carried out in all reservoirs except Kemnader See during the last 20 years [14].

Figure 1: Map of the area and the reservoir system studied on Ruhr River.

Mentions:
Molluscs were sampled at four out of the five artificial reservoirs on the river Ruhr: Hengsteysee, Harkortsee, Kemnader See and Baldeneysee (see map in Fig. 1 and Table 1 for details). Baldeneysee is the largest of the four, noticeably longer and with more than double the volume of the other reservoirs which are of similar size (Table 1). All reservoirs were constructed (three as early as the 1930's) as deposit reservoirs of sediments from the inflowing rivers Lenne and Volme and natural water purification. With the construction and development of more effective sewage treatment plants along the Ruhr the initial function of water purification has become secondary; currently the reservoirs of the Ruhr River serve for drinking water and hydropower supply and recreation. The shallow nature of these water bodies has gradually resulted in volume loss due to the deposition and accumulation of sediments. As a restoration measure, sediment removal has been carried out in all reservoirs except Kemnader See during the last 20 years [14].

Bottom Line:
Between-reservoir comparisons indicated an advanced eutrophication at Baldeneysee and Hengsteysee and the small-scale within-reservoir variations of component communities provided evidence that larval trematodes may have reflected spatial bird aggregations (infection 'hot spots').Two life history groupings of dominant species, the 'cyprinid' and 'anatid' parasites, that depict two aspects of progressive eutrophication in this mature reservoir system, were identified.Whereas variations in trematode community diversity and abundance may indicate the degree of eutrophication on a larger scale (among reservoirs), the infection rates of the two life history groups of dominant species, the 'cyprinid' and 'anatid' assemblages, may be particularly useful in depicting environmental variability, eutrophication effects and infection 'hot spots' on smaller spatial scales.

Background: Analysis of the data available from traditional faunistic approaches to mollusc-trematode systems covering large spatial and/or temporal scales in Europe convinced us that a parasite community approach in well-defined aquatic ecosystems is essential for the substantial advancement of our understanding of the parasite response to anthropogenic pressures in urbanised areas which are typical on a European scale. Here we describe communities of larval trematodes in two lymnaeid species, Radix auricularia and Lymnaea stagnalis in four man-made interconnected reservoirs of the Ruhr River (Germany) focusing on among- and within-reservoir variations in parasite prevalence and component community composition and structure.

Results: The mature reservoir system on the Ruhr River provides an excellent environment for the development of species-rich and abundant trematode communities in Radix auricularia (12 species) and Lymnaea stagnalis (6 species). The lake-adapted R. auricularia dominated numerically over L. stagnalis and played a major role in the trematode transmission in the reservoir system. Both host-parasite systems were dominated by bird parasites (13 out of 15 species) characteristic for eutrophic water bodies. In addition to snail size, two environmental variables, the oxygen content and pH of the water, were identified as important determinants of the probability of infection. Between-reservoir comparisons indicated an advanced eutrophication at Baldeneysee and Hengsteysee and the small-scale within-reservoir variations of component communities provided evidence that larval trematodes may have reflected spatial bird aggregations (infection 'hot spots'). Two life history groupings of dominant species, the 'cyprinid' and 'anatid' parasites, that depict two aspects of progressive eutrophication in this mature reservoir system, were identified.

Conclusions: We conclude that trematode communities in the lake-adapted R. auricularia are better suited for monitoring the effect of environmental change on host-parasite associations in the reservoir system on the Ruhr River and other similar systems due to the important role of this host in trematode transmission in lakes. Whereas variations in trematode community diversity and abundance may indicate the degree of eutrophication on a larger scale (among reservoirs), the infection rates of the two life history groups of dominant species, the 'cyprinid' and 'anatid' assemblages, may be particularly useful in depicting environmental variability, eutrophication effects and infection 'hot spots' on smaller spatial scales.